Well, I was having some oil pressure problems that I posted about a while ago. Check out the link for some details if interested. --> http://forums.corvetteforum.com/zerothread?id=668973.

Where I am at the moment
I've changed the oil pump to a Melling M55A and the problem remains. Is the next step to yank the motor and bring it to the machine shop or am I missing a step along the way.

Any thoughts?


Motor :smash:

 

While you had the pan down you should have checked the bearing clearances.
Before you rip the motor out I would drop the pan and check atleast the Rear Main clearance to see what you have.
Also I’m sure you already have but have you tried a different gauge, I didn’t see it in your last post.
I run a Fram filter and maintain 60 PSI at all times, RPMs and temps.
Plastigauge is cheap and will give you a good idea of your bearing clearances unless you have a problem with your cam bearings somewere.

 

I had a thought. I pickup was welded to the old oil pump about 3/4 of the way around - I think the other 1/4 is where the pressure release valve is. The pickup is currently tack welded to the new pump. Could the pump be sucking air where the pickup meets the pump at high RPMs?

I know some people epoxy the pickup to the pump for a total seal. Is it worth a shot?

 

I'll see if I can dig up a mechanical gauge this week and see if it shows the same thing.

I figured bad bearing clearances would affect oil pressure everywhere, not just at high RPM - but what do I know. Next time I drop the pan (this week probably) I try to check the rear main. Should be easy enough and the added info won't hurt.

 

At the RPMs you see the flucuation there are a few things that could be the cause.

Airation. Do you have a baffle or windage tray in the pan? Sounds like the pump is sucking some air.

Pick-Up Positioning: Is the pickup position 1/4" min to 3/8" max from the bottom of the pan? This positioning is crucial. Use a piece of modeling clay.

Sump Depth: Are you running the stock 5 quart pan? I've repeatedly heard that a HV pump can suck a stock pan nearly dry at high rpms; This occurs because gravity doesn't have enough time for the oil to drain back; much of the oil being trapped in the lifter valley and under the rocker covers. GF sells a 6 qt pan that will bolt in place; has a deeper sump. You'll need a different puckup though.

Anti-Cavitation Pump: Moroso and others sell a blue-printed oil pump with anti-cavitation grooves cut into the pump body and in the cover to eliminate cavitation and prevent spark scatter.

Clearance between the ends of the oil pump gears and the cover. Inspect the gear for any nicks or grooves which may have been caused by abrasive debris. I use to have to sand down the pump body to reduce the excessive clearance.

Gauge Accuracy: Someone already mentioned to install a mechanical oil pressure gauge to cross-check the accuracy of the stock one.

Hope this helps.

Jake


[Modified by JAKE, 12:49 PM 12/1/2003]

 

IS your dash reading accurate?Maybe the sender is going out?I think you can hook up a mechanical gauge and watch the oil pressure readings from there to compare to your dash read out...unless you already have that.A friend of mine had a bad dash reading making it look like oil pressure problems and it turned out to be one od the sensors or senders.Just something to check too.

:)

 

I don't think this is your problem most pumps are a press fit and the tack weld is just a security measure I had my pickup tack welded and am not expereincing any problems.

 

Guys, thanks for the feedback and info!

I'm currently using the stock oil pickup, an OEM type replacement pump (Melling M55A) which replaced the high volume pump, stock 5 quart pan with the baffle in it but I'm not using the stock windage tray. The engine builder was hesitant to use the windage-tray/main-cap-studs because he had already bored the block with the existing main cap bolts. But it's worth looking into again.

Basically, the entire oiling system is stock minus the windage tray.

This weekend I'll borrow a mechanical gauage and check it out. If that doesn't pan out (heheh get it... oil...pan... sorry) I'll check into the windage tray since hopefully it should be easy enough to bolt back on. Lastly, I'll look into a pan with a high capacity before I pull the motor.

My favorite part about owning the car is beating the snot out of it. With out that the fun diminishes a tad.

The fun continues.

-Mike